Depending on your unit, they might require you to wear a certain kind. We actually wore straight up cotton for my first couple years (in Minnesota in the winter, so everything was wrinkly all the time) before they got smart and had us wear CNTs. I'd wait until you've started to make sure you're not wasting money.
Personally, I think poly-wool is WAY more comfortable than CNTs, and the sewn in creases look sharp in my opinion. Don't have a brand recommendation for ya, though, since I haven't cared enough to notice the difference.
My NROTC unit had an unwritten rule that underclassmen wore wash khakis and 2/c and 1/c mids could wear CNTs or poly-wools if they purchased them on their own.
If you know they're kosher, poly-wool is the way to go in my opinion.